Development of Serological Assays and Seroprevalence Studies of the New Coronavirus 2019 (COVID-19): Reports from Saudi Arabia

Abstract

Serological assays are valuable tools for tracking COVID-19 spread, estimation of herd immunity, and evaluation of vaccine effectiveness. Several reports from Saudi Arabia describe optimized in-house protocols that enable detection of SARS-CoV-2 specific antibodies and measurement of their neutralizing activity. Notably, there were variations in the approaches utilized to develop and validate these immunoassays in term of sample size, validation methodologies, and statistical analyses. The developed enzyme-linked immunoassays (ELISAs) were based on the viral full-length spike (S), S1 subunit, and nucleocapsid (NP), and enabled detection of IgM and/or IgG. ELISAs were evaluated and validated against a microneutralization assay utilizing a local SARS-CoV-2 clinical isolate, FDA-approved commercially available immunoassays, and/or real-time polymerase chain reaction (RT-PCR). Overall, the performance of the described assays was high, reaching up to 100% sensitivity and 98.9% specificity with no cross-reactivity with other coronaviruses. In-house immunoassays, along with commercially available kits, were subsequently applied in a number of sero-epidemiological studies aiming to estimate sero-positivity status among local populations including healthcare workers, COVID-19 patients, non-COVID-19 patients, and healthy blood donors. The reported seroprevalence rates differed widely among these studies, ranging from 0.00% to 32.2%. These variations are probably due to study period, targeted population, sample size, and performance of the immunoassays utilized. Indeed, lack of sero-positive cases were reported among healthy blood donors during the lockdown, while the highest rates were reported when the number of COVID-19 cases peaked in the country, particularly among healthcare workers working in referral hospitals and quarantine sites. In this review, we aim to (1) provide a critical discussion about the developed in-house immunoassays, and (2) summarize key findings of the sero-epidemiological studies and highlight strengths and weaknesses of each study.

A potential association between obesity and reduced effectiveness of COVID‐19 vaccine‐induced neutralizing humoral immunity

“…[24][25][26][27][28] It is also vital to note that SNT in many instances, ). 31,[37][38][39][40] We also found 11 recovered cases (6 with normal BMI and 5 with various degree of obesity) with confirmed PCR diagnosis tested negative for IgG NP-ELISA which supports previous studies that reported antibody waning following recovery. 37,41,42 These results demonstrate the potential vulnerability of recovered patients to reinfection and highlight the importance of vaccination uptake for this population.…”

“…Since the pandemic started, many studies reported asymptomatic cases with lack of self‐awareness which probably increased due to the emergence of variants with high transmissibility and mild pathogenicity (e.g., Omicron; B.1.1.529). 31 , 37 , 38 , 39 , 40 We also found 11 recovered cases (6 with normal BMI and 5 with various degree of obesity) with confirmed PCR diagnosis tested negative for IgG NP‐ELISA which supports previous studies that reported antibody waning following recovery. 37 , 41 , 42 These results demonstrate the potential vulnerability of recovered patients to reinfection and highlight the importance of vaccination uptake for this population.…”

“…All samples were subjected to in house ELISAs that enable sensitive and specific detection of human IgG antibodies directed against either SARS‐CoV‐2 S or NP antigen. 29 , 30 , 31 It is important to note that all participants have received two doses of homologous or heterologous doses of the following COVID‐19 vaccines: BNT162b2 by Pfizer‐BioNTech, ChAdOx nCov‐2019 by AstraZeneca, or mRNA‐1273 by Moderna. All three vaccine types mount host immune response exclusively to SARS‐CoV‐2 S protein.…”

“…Both assays offered up to 100% sensitivity and ≥98.4% specificity. 29 , 30 , 31 The cut‐off optical density values at 450 nm for the S and NP assays are 0.27 and 0.17, respectively. 29 , 30 All sera collected in this study were screened for the presence of SARS‐CoV‐2 specific antibodies utilizing these in‐house ELISAs.…”

Lack of Evidence on Association between Iron Deficiency and COVID-19 Vaccine-Induced Neutralizing Humoral Immunity

“…Iron deficiency (ID) is a global health problem that affects nearly two billion people [ 1 ], and iron deficiency anemia (IDA) is considered the topmost leading cause of anemia worldwide [ 2 ]. The prevalence of ID and IDA is generally higher in women of child-bearing age, preschool children, and individuals with low socioeconomic status [ 1 , 3 ]. The underdeveloped regions have a five-time higher prevalence rates of ID and IDA compared to the developed nations [ 4 ].…”